1. Field of the Invention
This invention relates to fuel elements for nuclear reactors and, more particularly to locking nut structures for fuel element end fittings, and the like.
2. Description of the Prior Art
To generate power, a charge of uranium is disposed within the core of a nuclear reactor, usually in uranium dioxide pellets that are loaded into metal tubes, or fuel rods. Groups of these fuel rods are assembled into fuel elements in which the fuel element structure supports the rods and maintains a proper spacing between these rods to enable pressurized water, or any other suitable coolant, to flow past the rods and absorb from the rods the heat that is generated through the nuclear processes that occur in the uranium.
Because the fuel rods usually are supported vertically, that is, with the central axes of the tubes perpendicular to the earth's surface, the tube ends are positioned between "upper" and "lower" end fittings. In some types of fuel elements, these end fittings support the associated fuel rods by restraining these rods between the two fittings. A number of techniques have been divised to join the end fittings into an integral fuel element. Typically, members that extend beyond the length of the fuel element have threaded ends which protrude through the end fittings. Special nuts are torqued onto the threaded ends and, in this manner, join the end fittings to the balance of the fuel element structure.
Because of the dynamic forces that characterize the coolant flowing through the fuel element, thermal expansion and contraction, and the like, there is a genuine possibility that one or more of these nuts might work loose and fall off the fuel element, thereby weakening the fuel element and doing possible damage to the reactor system. To prevent this from occuring, proposals have been advanced to weld the nuts to the end fitting in order to insure that the nuts will not disengage the threaded end of the member to which it joined.
The need nevertheless arises to remove these nuts in order to disassemble fuel elements for any number of reasons, e.g., failed fuel rod location, inspection and replacement. Frequently, the nuts must be unthreaded using remote handling equipment because of the radioactive environment. In these circumstances the difficulties and expense of fuel element disassembly and assembly are compounded by these designs in which each nut must be handled separately.
Accordingly there is a need to provide some means for engaging the ends of the members that protrude through the end fittings without risking broken or loose parts within the reactor system. It is clear that there also is a need for a more efficient way to engage and disengage the nuts with these threaded ends that is specifically adaptable to remote handling equipment and procedures.